vize1 = input("1. Vize:")
vize2 = input("2. Vize:")
Final = input("Final:")
sonuc = int(vize1)*(3/10) + int(vize2)*(3/10) + int(Final)*(4/10)
if(sonuc >=90):
print("AA")
elif(sonuc>=85):
print("BA")
elif(sonuc>=80):
print("BB")
elif(sonuc>=75):
print("CB")
elif(sonuc>=70):
print("CC")
elif(sonuc>=65):
print("DC")
elif(sonuc>=60):
print("DD")
elif(sonuc>=55):
print("FD")
elif(sonuc>=50):
print("FF")